The invention relates to a method for cleaning stone and metal surfaces and an apparatus for carrying out said method. In particular the invention relates to a method and an apparatus for cleaning surfaces of stone and metal contaminated and corroded by atmospheric influences, for example facades of this type or stone and metal monuments.
The stone surfaces cleaned according to the invention may be both artificial stone surfaces such as concrete surfaces or also natural stone surfaces such as limestone surfaces or granite surfaces.
Because of pronounced air pollution the cleaning of such surfaces like the surfaces of monuments or statues cast usually from bronze is becoming of increasing importance. As a rule, when cleaning such surfaces only the dirt and soil layer should be removed. Usually, the metal layer therebelow corroded by atmospheric pollutants is to be retained.
The important point is to remove as little material as possible. In particular, the stone or metal material disposed therebelow must not be removed. In the case of bronze figures not even the natural patina, if any is present, should be removed.
A cleaning method having the features of the preamble of claim 1 is known from U.S. Pat. No. 3,427,763. In this known cleaning method a pressurized water flow generated by means of a water pressure between 100 and 900 bar in a mixing chamber sucks the blast material in from a passage opening laterally into the mixing chamber, said blast material having a granulation between 0.01 and about 3 mm and consisting of sand, quartz, corundum, flue dust and the like. The water jet acts as water jet pump and in this manner draws in the blast material particles.
The intention is that because the blast material particles are carried by a water jet and thrown against the surface to be cleaned that the blast material particles do not simply strike against said surface to be cleaned. On the contrary, at least mainly, they are to be entrained by the sprayed-on water, slide along the surface and in this manner clean the surface.
An essential disadvantage of this known method is that too much of the material to be worked is removed. Accordingly, the known method is used primarily for cleaning coarse parts, such as castings and the like, and in addition also as separating cutting method in which the water jet charged with blast matrial saws a gap through the workpiece to be severed. Thus, the known method is not suitable for cleaning valuable objects, for example historical buildings, monuments and the like. It is not possible in practice to conduct the known method so that only the upper layer to be removed is in fact removed and the material therebelow is not impaired.